1. Field of the Invention
The present invention relates to a common interface controller, in particular for use in a digital television device such as a receiver, and a method of descrambling transport stream channels, in particular descrambling channels of first and second transport streams using a conditional access module.
2. Description of the Related Art
It is known to provide a digital television receiver having a connector for an external conditional access module allowing the conditional access module to be selectively attached and detached. This allows a consumer to purchase a digital receiver which is not tied to a particular service provider and then to attach a conditional access module as appropriate.
Digital television receivers are provided with a tuner to obtain the transport stream in which a desired channel is found. An example of a channel is a television programme, such as BBC 1, possibly together with its associated teletext or such like. The transport stream is then passed to the conditional access module so as to allow the desired channel to be descrambled.
It is also possible to provide a digital television receiver with two or more tuners for obtaining respective transport streams. This allows more than one channel to be used simultaneously, for instance allowing the recording of one channel whilst watching another or providing picture-in-picture display. Although many conditional access modules are capable of descrambling more than one channel simultaneously, these conditional access modules generally process only one transport stream. Unfortunately, there is no guarantee that both desired channels will occur in the same transport stream. Therefore, to ensure the possibility of descrambling two channels, it is necessary to provide a digital television receiver with two of the conditional access modules, each for processing a respective transport stream.
The need for two conditional access modules and the additional costs involved are clearly undesirable.
U.S. 2002/0101991 A1 proposes a system in which two transport streams are multiplexed together and provided to a single conditional access module. However, the conditional access module itself must be non-standard in order to deal with two transport streams. Furthermore, the connector and interface must allow additional information to be sent from the receiver to the conditional access module so as to indicate to which of the transport streams each respective packet of data belongs.